In constructing a multicolor silver halide photographic element primary reliance for analysis of performance is still placed on characteristic profiles of the type first suggested by Hurter and Driffield in the nineteenth century. An ideal characteristic profile is shown in FIG. 1, wherein optical density (hereinafter referred to as density) is plotted against log exposure. The characteristic profile CP produced by varied levels of exposure of a photographic element followed by processing and processing provides a valuable insight into the photographic performance to be expected in imaging. Exposures less than received at point A, just to the left of the toe of the characteristic profile, do not give rise to any increase in density. The displacement of the characteristic profile above zero density is referred to as minimum density (Dmin) or fog. Useful imaging occurs at exposures between points A and B. Exposures higher than those at point B, lying just to the right of the shoulder of the characteristic profile, produce no further increase in density. Point B lies at the highest attainable density, referred to as maximum density (Dmax). For the purpose of comparing photographic element speeds a reference point such as C is selected on the characteristic profile, typically at about 0.01 density unit above fog. The slope of the characteristic profile (.DELTA. density/.DELTA.log E), referred to as contrast or .gamma., usually measured over some segment of the curve CP bridging mid-scale density also provides valuable information on imaging characteristics. Toe contrast, measured in the A to C toe region of the characteristic profile, and shoulder contrast, measured in the D to B shoulder region of the characteristic profile, also provide useful measures of imaging properties. The displacement along the exposure scale of points A and B determines the exposure latitude of the film. The longer the exposure latitude the lower the risk image information being lost through over or under exposure during imaging. The accepted units of exposure (E) are lux (previously, meter-candle)-seconds. Each 0.3 increase in log exposure doubles the exposure and is referred to by photographers as a "stop". A half stop is 0.15 log E.
In constructing a multicolor photographic element the aim is usually to construct an element capable of producing at least three distinct characteristic profiles, indicative of the a yellow dye teristic profile produced by blue light exposure, a magenta dye characteristic profile produced by green light exposure and a cyan dye characteristic profile produced by red light exposure. The aim is usually to produce yellow, magenta and cyan profiles that are as nearly superimposed as possible. This is facilitated by characteristic profiles for each of the color records that are as nearly linear as possible over the intended exposure range. For example, in characteristic profile CP the linear portion of the characteristic profile between points C and D is ideal for color imaging, since a linear profile within an acceptable working exposure range facilitates superposition of yellow, magenta and cyan profiles and maintenance of an accurate color balance at varied levels of exposure.
Although the image dye characteristic profiles of a multicolor photographic element are useful in assessing its imaging qualities, one important image property that requires separate inquiry is image noise--i.e., granularity. It is generally recognized that photographic speed increases with increasing silver halide grain sizes and that image granularity also increases with silver halide grain sizes. The object in constructing multicolor photographic elements is usually to satisfy imaging application speed requirements while providing images of lowest attainable granularity.